PROBLEM TO BE SOLVED: To support motions of a knee joint and a hip joint at a good timing.SOLUTION: A bending and stretching motion support device 10 includes a seat part 20, a pedestal 30, a bending and stretching mechanism 40, and a control unit 50. The seat part 20 is formed in a flat plate shape and is supported by the bending and stretching mechanism 40 so as to move upward and downward. The control unit 50 includes a seat part height setting part 52, a manual operation switch 54, a radio communication part 56, a motor driving part 58, and a control part 60. The radio communication part 56 receives a radio signal of a biological signal (bioelectric potential) reflecting an intention of a stretching or bending motion transmitted from a radio communication unit 80 worn by a trainee P. The control part 60 includes determination means for executing control processing and determining whether or not the trainee P is prepared to perform a rise operation based on the received biological signal. When it is determined that the trainee P is prepared to perform a rise operation, a control signal for starting motor driving is output to the motor driving part 58.
